For many years, materials have been treated for various purposes such as fireproofing, rust inhibiting and priming. Many of the treatment methods that utilized asphalt based products involve the inhibition of oxidation of the treated metal. One such use of petroleum based paint product used to inhibit corrosion is disclosed in Troutman U.S. Pat. No. 4,406,704. Troutman discloses an air dryable corrosion inhibiting primer which limits the amount of volatile organic compounds that are emitted into the atmosphere by reducing the solvent content. This relatively environmentally friendly primer consists of an air dryable synthetic alkyd resin, an organic solvent, a suspending agent, polar additives, a wetting agent, coloring pigments, a dryer, an extender pigment and a corrosion inhibitor such as calcium borosilicate.
Another type of corrosion resisting composition containing asphalt is claimed in Miller U.S. Pat. No. 3,549,391. Miller discloses corrosion proofing composition which can be used for rust proofing undersides of cars. The rustproofing asphalt based sprayable coating consists of asphalt, mineral fillers, a metal soap of a waxy hydrocarbon oxidate and an organophilic modified clay.
Cogliano U.S. Pat. No. 4,503,106 discloses a sheet-like barrier which can be used for insulation and waterproofing purposes. The construction board barrier consists of an adhesive bituminous material and may contain a layer of asphalt.
Another well known anti-corrosion metal treatment method is the coating of a metal with a terne alloy. Terne is a term used to describe an alloy containing about 10% tin and 90% lead. The terne plate is conventionally applied to a ferrous metal by immersing the ferrous metal in a molten bath of terne metal. The terne coating is primarily used to reduce the formation of ferrous oxides in the metal so as to prevent corrosion and extend the life of the metal. Since both lead and tin are relatively stable elements, the lead and tin oxidize very slowly even in harsh environments. As a result, the terne alloy is an excellent protective coating that requires little, if any, maintenance and significantly inhibits the oxidation of ferrous compounds in the metal. Because of the excellent anti-corrosion qualities of terne coated metals, ferrous metal coated with a terne alloy are commonly used in metal roofing, metal siding and other industrial applications where unprotected metals would exhibit high corrosion rates.
Although terne coated metals have excellent corrosive resistive properties, the terne coating when initially applied has several adverse properties when used in certain applications. Terne coated metals are commonly used as roofing materials in both civilian and military airports. Metals that are newly coated with a terne alloy have been found to have a high reflectivity of both visual light and electromagnetic waves such as used in radio transmissions. This high reflective property of newly coated terne when used for building materials in airports, especially roofing materials, adversely effects the radar and communication in the surrounding area. Furthermore, glare of the sun caused by the relatively high reflectivity of the terne coating can cause temporary visual impairment when the pilot is taking off or landing at the airport.
The high reflective properties of metals that have been newly coated with a terne alloy continues until the terne coating begins to oxidize. The oxidation of terne coating is commonly known as weathering. As the terne alloy begins to weather, a layer of lead oxide and tin oxide forms on the terne coating. The lead and tin oxide layer is known also as a patina formation. Consequently, weathering of the terne coating is essentially the corrosion of the terne alloy. Since lead and tin are relatively inert, the complete corrosion of the terne coating takes a very long time. The life of the terne coating is further extended by the formation of the lead oxide and tin oxide on the terne alloy. The lead and tin oxides essentially act in of itself as a protective barrier to the terne coating. The lead and tin oxide layer significantly reduces the amount of oxygen or moisture that comes in contact with the non-oxide terne coating by acting as a stable barrier against the adverse elements. The oxided layer of lead and tin further increase the time necessary to adequately weather the terne. Due to the stability of lead and tin, terne coating which is exposed to the atmosphere normally takes approximately ten years before the alloy is considered to be completely weathered, a condition which is highly desirable for roofing and other building applications.
The lead and tin oxide formation or patina formation on the terne coating exhibits a duller appearance than newly terne coated metals. The patina formation on the terne alloy is significantly less reflective to both visible light and electromagnetic waves. Consequently, weathered terne is preferable to newly coated terne for building and roofing materials, especially used in airports and military facilities. Since the patina formation on terne takes about ten years to form to a point whereby the terne coating is not unduly reflective to visible light and electromagnetic waves, many industries have either refused to use terne coated materials or have attempted to artificially reduce the terne's reflective properties. Storing the terne coated steel for about ten years is infeasible due to the cost, time and space requirements.
One common method to overcome the adverse effects of high reflectivity of the terne coating has been to treat the terne coating with a less reflective substance. Normally paints are used containing dull, non-reflective pigments. However, the use of paint to disguise the reflective nature of the terne is normally an unsatisfactory and expensive solution. Paints are normally designed to be a protective layer to the material it is applied to. Paints such as those disclosed in Miller and Troutman normally contain some type of corrosion inhibiting ingredients to prevent oxidation of the metals the paint is applied to. When such a paint is used on terne coating, oxygen and moisture are sealed off from the terne surface. As a result, the terne coating never has a chance to oxidize. Consequently, when the paint begins to deteriorate and peel away, the non-oxidized high reflective terne coating is again revealed. As a result, the paint surface must continuously be maintained to prevent the adverse reflective effects of the non-oxidized terne coating. The time, effect and expense to maintaining the paint on the terne coating reduces the desire to use terne coated metals. As a result of the inadequate and expensive remedies to reduce the reflectivity of non-oxidized terne metal, there has been a demand for a method to accelerate the weathering of terne coated metals.